One difficulty with present magnetic resonance imaging techniques and systems is that the image is limited to orthogonal planes. This means that the image plane can only be made parallel to the faces of a cube. In order to fully realize the capabilities of magnetic resonance imaging, it is necessary to create an image at any arbitrary orientation. Theoretically, as discussed in the General Electric booklet entitled: NMR: A Perspective on Imaging, published in 1982 by the General Electric Company Medical Systems Operations of Milwaukee, Wis., by adjustment of the gradient system which produces the spatial linear field gradients crucial to NMR imaging, a "tilted gradient" may be provided. The General Electric booklet states that this is implemented by "suitably combining two or all three gradients."
However, it has not been practical to obtain an image of an arbitrary angular orientation, because of non-idealities in the NMR system. For example, in a heart scan it might be desirable to make images of the outer surface of the heart at different angles. With present NMR techniques this is not possible.